Question

How many grams of NaOH should be added to water to prepare 250ml solution of 2 M NaOH?

Answer 1

this is based on conecpt of molarity                                                                                             molarity = mole of solvent /volume of solution in L                                        here,                                                                                                                       molarity of solution=2M                                                                                         volume of solution =250m
hence,                                                                                                                             2M =mole of NaOH/[250 /1000]
mole of NaOH=0.5
weight in gram = 0.5 *40 gram =20 gram

Answer 2

20 g of NaOH should be added to water to prepare 250 ml solution of 2 M NaOH.

Solution:

Molarity is defined as the amount of moles of a compound dissolved in an amount of solvent.

$Molarity\quad (M)\quad =\quad \frac { Moles\quad solute }{ Litre\quad of\quad solution }$

From the given,

Molarity of solution = 2M

Volume of solution = 250 ml

Moles of NaOH present in 250 ml of 2M solution $=\quad 2M\quad \times \quad \frac { 250 }{ 1000 } \quad =\quad 0.5\quad mol$

Molar mass of NaOH = $40 \frac { g }{ mol }$

$Mass\quad of\quad 0.5\quad mol\quad NaOH\quad =\quad 0.5\quad \times \quad 40\quad =\quad 20\quad g$